1. Field of the Invention
This invention relates to a process for removing oils from oily waste water streams. More particularly, this invention relates to a process for removing oil from aqueous refinery streams wherein the oil is present in the stream as free oil and as an oil-in-water emulsion, the oil being removed from the water by passing the stream over a particulate bed of vinyl chloride containing polymers such as PVC and its copolymers. Still more particularly, this invention relates to the removal of oil from oily refinery streams wherein the oil is present as a relatively stable oil-in-water emulsion and wherein said streams may be sour water from a steam cracker or spent caustic from steam cracker treating towers and wherein the stream is filtered through a bed of unprocessed, powdered PVC homopolymer or its copolymers such as PVC, Saran (a vinyl chloride-vinylidene chloride copolymer) and polyvinyl chloride-polyvinyl acetate.
2. Description of the Prior Art
Increasing world population and concomitant expansion of industrial output has placed continuously increasing demands on industry to curtail environmental pollution and, at the same time, to make more efficient use of natural resources. One of the most meaningful and relevant goals of any industry is to decrease and even eliminate environmental pollution while at the same time reduce consumption of natural resources by using waste products of one industry as the raw materials for other industries, thereby effectively recycling material and industrial resources.
Aggressive industrialization has resulted in particularly acute demands for oil and oil-derived products, particularly petroleum oil and its products, such as gasoline, fuel oils, chemicals, plastics, etc. Pollution of the surface of the sea due to spillage from tankers and leakage from offshore drilling facilities has received much attention in recent years because of the immediately visible destruction of the natural environment including beaches, fish, local wild life, etc. Another, but less publicized area of environmental pollution from oily wastes derives from the aqueous effluent of oil refineries, chemical plants, cleaning operations, etc. This can be particularly difficult to deal with as opposed to oily spills on sea water, because these oils are often present as a relatively stable oil-in-water emulsion. Such emulsions are fairly stable and are consequently difficult to break and separate from the water in an economical, efficient manner.
Free oil, as well as oil that is in suspension or as a relatively unstable oil-in-water emulsion, can readily be separated from the oil-contaminated water by various physical or mechanical processes, such as screen-type filters or coalescers followed by some sort of settling tank wherein the oil rises to the surface and can be skimmed off using ribbon skimmers, etc. However, these methods do not work with relatively stable oil-in-water emulsions. In order to break or demulsify a more stable emulsion, one must resort to chemical separation means such as adding ionic salts or a water-insoluble solvent for the oil, such as ethers. This will break the emulsion. In either case, however, the cure can be more environmentally detrimental than the disease, as well as rendering the recovered water unsuitable for further use by industry without having to resort to additional purification steps in order to remove the additives added to same in order to break the emulsion.
One of the major sources of oily water in the petroleum industry comes from the sour water effluent of steam cracker primary fractionator tower overheads, which contain highly olefinic, emulsified and free oil, as well as spent caustic from steam cracked liquid and vapor treating towers containing relatively stable but highly reactive, olefinic, polymerizable oil.
Thus, there is a recognized need in the industry for a relatively efficient and economic method of breaking these relatively stable oil-in-water emulsions and to separate the oil therefrom so that the waste waters can either be recycled to other refinery areas or industries, or fed to sewers in a relatively oil free form to avoid environmental pollution.